Constraining new physics with a novel measurement of the 23Ne β-decay branching ratio

Measurements of the beta-neutrino correlation coefficient (aβν) in nuclear
beta decay, together with the Fierz interference term (bF ), provide a robust test for the existence of exotic interactions beyond the Standard Model
of Particle Physics. The extraction of these quantities from the recoil ion
spectra in β-decay requires accurate knowledge, decay branching ratios, and
high-precision calculations of higher order nuclear effects. Here, we report
on a new measurement of the 23Ne β-decay branching ratio, which allows
a reanalysis of existing high-precision measurements. Together with new
theoretical calculations of nuclear structure effects, augmented with robust
theoretical uncertainty, this measurement improves on the current knowledge
of aβν in 23Ne by an order of magnitude, and strongly constrains the Fierz
term in beta decays, making this one of the first extractions to constrain both
terms simultaneously. Together, these results place bounds on the existence
of exotic tensor interactions and pave the way for new, even higher precision,
experiments.